1. Technical Field
The present invention relates to a technique of creating a color conversion table and a device profile.
2. Related Art
The color conversion table is information that represents a correspondence relationship between an input color coordinate system and an output color coordinate system. Coordinate values of the input color coordinate system of the color conversion table represent positions of points in the color space of the input color coordinate system, and coordinate values of the output color coordinate system represent positions of points in the color space of the output color coordinate system. In addition, in the present specification, an arbitrary point in the color space is referred to as a “color point” or “grid point”. Further, the color point, represented by an input value registered in the color conversion table, and the color point, represented by an output value registered therein, are respectively referred to as an “input grid point” and an “output grid point”.
As a technique of a smoothing arrangement of the input grid points and the output grid points of the color conversion table, for example, there is a technique disclosed in JP-A-2006-197080 by the applicants of the present application. In this smoothing, after the grid points of the Lab color coordinate system are shifted, through an optimization process using an objective function, an ink amount which is optimal to reproduce L*a*b* grid points after the shift, is determined. The optimal ink amount is determined as an ink amount minimizing the objective function.
Further, as a known conversion table setting method, there is a method of setting a conversion table corresponding to a certain medium among multiple kinds of media, each having a known conversion table which is used as a reference when the input picture data is converted into print data, as a conversion table corresponding to a medium whose type is unknown (JP-A-2009-220356).
However, for each type of the printing media, the color development characteristic (color value characteristic) in a case of using the same ink amount is different, and the ink amount (duty limit) which can be adhered onto a unit area is different. For this reason, there is a problem in that it is necessary to provide an objective function for each type of printing media in order to create a color conversion table for each of the multiple printing media. Further, the objective function includes a term for rating picture quality on the basis of color values of reproduced colors when inks with respective ink amounts are adhered onto a printing medium. For this reason, there is a problem in that a color prediction model, which is for predicting color values on the basis of the amounts of ink, and the like have to be provided for each type of printing media. However, great efforts and resources are necessary to provide the color prediction model and the like in advance for each type of printing media, and originally it is difficult to provide the color prediction model and the like for an unknown printing medium. Accordingly, until now, particularly, as for a printing medium which is arbitrarily selected by a general user in his house or working place, even when the color conversion table defining amounts of ink for reproducing favorable colors on the printing medium is intended to be created, there is the above-mentioned restriction (the restriction that it is difficult to provide the color prediction model and the like corresponding to the printing medium which is arbitrarily selected), and thus it has been difficult to create an optimal color conversion table. Further, in JP-A-2009-220356, the conversion table corresponding to the medium included in the multiple types of media each having a known conversion table is substituted for a conversion table corresponding to an unknown type medium. Hence, it is difficult to create a color conversion table most appropriate for the printing medium which is arbitrarily selected by a user.
Further, when a printing process is performed by using the color conversion table or the device profile which is created by a user, the user may not satisfy the printing result (picture quality). In such a case, although the user intends to perform a certain process for obtaining a satisfactory printing result, it is difficult for the user, who is largely inexperienced at the printing process, to know which process should be performed for which printing result.